1. Field of the Invention
The present invention relates to a heat-hardenable composition, a heat-sensitive recording material and a planographic form plate using the composition. More specifically, the present invention relates to a heat-hardenable composition having excellent storage stability and hardenability, a heat-sensitive recording material utilizing the thermally cross-linkable property of the composition, particularly a heat-sensitive recording material capable of being used as a material for a planographic printing plate in a direct plate making process in which the material is directly inscribed by scanning an infrared laser, and a planographic form plate using the heat-sensitive recording material.
2. Description of the Related Art
Traditionally, the technology of a heat-hardenable resin, which can be cross-linked by the action of heat, is so versatile that it has been used in a variety of applications including the production of paints, ink, rubber, adhesives, and the like, textile processing in the field of textile materials, the production of sealing materials in the field of electronics related materials, and printing and resist production. As to materials for the traditional heat-hardenable resins and their application in ink, rubber, and adhesives, details are described in a number of textbooks. An example of the textbooks is "Handbook of cross-linking agents", edited by S. Yamashita et al, Taiseisha Publishing Co., Ltd. (1981). Application of a heat-hardenable resin in printing is described in, for example, Japanese Patent Application Publication (JP-B) No. 45-23,519.
As to the application to photosensitive recording materials, solid-state and semiconductor lasers, which emit infrared light of wavelengths range from 760 to 1200 nm, are recently attracting attention as a recording light source in a system where plates are made directly from digital data of a computer, because these radiation sources, which have a high output power despite their small size, can be easily obtained. However, since the sensitivities of many practically useful photosensitive recording materials are limited to light in a visible light region of 760 nm or less, the above-mentioned infrared lasers cannot be used for image recording. Accordingly, there is a demand for an image recording material which can be recorded on by an infrared laser.
Meanwhile, an example of a negative-type image recording material, which can be inscribed for recording by such an infrared laser, is described in Japanese Patent Application Laid-Open (JP-A) No. 8-276,558. This recording material comprises a substance which generates heat by absorbing light, an alkali-soluble resin, and a specific phenol derivative which has 4.about.8 benzene nuclei in the molecule. The drawback of this recording material was that the sensitivity of the material to a laser was insufficient. Despite many proposals to increase the sensitivity of the recording material, the material has been associated with the problem that in general measures to increase sensitivity tend to impair the storage stability of the recording material, and in particular, the storage stability in highly humid conditions.
Accordingly, there has been a strong demand for a hardenable material as an image recording material which has superior storage stability especially in such applications as materials for a heat-sensitive planographic printing plate and the like.